Motor with an electrically commutated stator and a rotor with permanent magnets

ABSTRACT

A low-noise, torque compensated motor with an electrically commutated stator and a permanent magnet rotor which is achieved solely through a spacing of the air gap surfaces of the stator if these surfaces are at least partially provided with fine gearing teeth and pole pairs are formed in which at least part of the fine gearing teeth are respectively offset in relation to one another.

PRIOR ART

The invention relates to a motor that has a stator with different magnetpoles and has a rotor with a matched number of permanent magnet poles,in which the air gap surfaces in the region between the stator and rotorare provided with fine gearings in order to reduce the torque betweenthem.

A similar motor has been disclosed by U.S. Pat. No. 3,604,961. In thisinstance, the electrically excited rotor, which is embodied as aninternal rotor, has a uniform, meander-shaped fine gearing teeth on itscircumference so that it is designed to be radially symmetrical in thisdirection. The poles of the stator are embodied as permanent magnets,but are not disposed uniformly in the circumference direction since theyalternatingly assume an angle of less than and greater than 360°/ç,wherein ç represents the number of poles. The deviation angle is thenselected so that a more uniform magnetic field distribution is producedin the circumference direction between the rotor and the stator. Thisleads to the reduction of the torque between the rotor and stator.Without this offset of the permanent magnets, the numbers of poles wouldcause a number of non symetrical to be produced between the rotor andstator, which could be detected when manually spinning the rotor andcould result in an unsteady and noise-encumbered operation of the motor.

This known reduction of the torque, however, requires a complex designof the stator which depends on the precise installation of the permanentmagnets. Furthermore, this design of the motor more or less limits thereduction of the torque.

An object of the invention is to produce a motor with compensation ofthe torque, which is simple in design and operationally reliable andwhich offers a significantly improved potential for reduction andcompensation of the torque.

The offsetting of the fine gearing teeth in the vicinity of the air gapsurfaces of the stator produces a symmetrically designed permanentmagnet rotor which is simple to manufacture and produces definitemagnetic field ratios in the circumference direction that can beinfluenced in a number of ways via the fine gearing teeth disposed onthe stator. In this connection, the stator can still be designed asessentially symmetrical. The compensation of the torque remains limitedto the design of the fine gearing, teeth which can be produced togetherwith the formation of the magnet poles by means of a simple stamping ofa “solid armature”. Therefore other improvements of the torquecompensation can also be easily incorporated into the manufacturingprocess of the motor since only the stamping procedure needs to becorrespondingly modified. Moreover, a power supply by means of slidingcontacts is no longer necessary since this can take place by means of asimple electronic control circuit.

A particularly simple design of the motor is produced by virtue of thefact that the number of magnet poles of the stator corresponds to thenumber of permanent magnet poles of the rotor, wherein the provision ismade in particular that the stator is embodied as an internal stator andthe rotor is embodied as an external rotor.

According to one embodiment, the effective compensation of the torque isproduced by the fact that the offset of the fine gearing of the polepairs identically and preferably corresponds to half a spacing of thefine gearing teeth.

With regard to the design of the rotor, according to one embodiment, theprovision can be made that the permanent magnet poles of the rotor areconstituted by means of individual permanent magnets that aredistributed uniformly over the circumference of the rotor and that havea polarity that alternates in the circumference direction, wherein theindividual permanent magnets can also be magnetized in a single-polefashion.

Another embodiment for the rotor can be produced by the fact that thepermanent magnet poles of the rotor are constituted by a number oftwo-pole annular segment permanent magnets distributed uniformly overthe circumference of the rotor, which are disposed with their poles inthe same direction toward the circumference, wherein the permanentmagnet poles can also be constituted by multi-pole annular segmentpermanent magnets.

The fine gearings are embodied as meander-shaped in a known fashion,where in the simplest case, the teeth and the tooth spaces of the finegearing teeth have identical widths and depths.

An extensive compensation of torque is produced by the fact that theteeth and the tooth spaces of the stator have different widths, but haveidentical depths and are supplementary to each other in the pole pairs,or by virtue of the fact that the widths of the teeth of the one poleand the tooth spaces of the other pole of the pole pairs of the statorchange in the same manner, at least in a partial region of thecircumference. The number of the teeth and tooth spaces of the statorpreferably is an integral multiple of the number of pole pairs formed.

The pole pair formation and the compensation of the torque can beembodied so that the teeth of the pole pairs of the stator, which areconstituted by respectively adjacent or diametrically opposed magnetpoles, are respectively offset in relation to one another and on theother hand, can be embodied so that the teeth of pole pairs of thestator, which are constituted by magnet poles respectively offset by twopole spacings, are respectively offset from one another. In bothinstances, the teeth of the pole pairs are offset in antiphase in thecircumference direction. In the event of a fixed or continuouseccentricity of the rotor, however, the effectiveness of thecompensation is limited.

In higher-poled motors, it is more favorable to dispose the teeth inantiphase by a double pole line, as the second embodiment demonstrates.

The influence of the rotor eccentricity is canceled out in these motors.

For the effectiveness of the compensation of the torque, theadvantageous provision should be made that the depth of the teeth andthe tooth spaces should be greater than or equal to the air gap widthbetween the stator and the rotor.

The invention will be explained in detail in conjunction with exemplaryembodiments depicted in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 show the design, in stages, of the stator for a given8-pole permanent magnet rotor,

FIG. 5 shows the formation of pole pairs from diametrically opposedmagnet poles, and

FIG. 6 shows the formation of pole pairs from magnet poles that areoffset by two pole lines.

The design of a motor with eight magnet poles P1 to P8 on theelectrically commutated stator St and eight permanent magnet poles M1 toM8 on the rotor R, respectively, is explained in conjunction with FIGS.1 to 4, wherein the figures respectively show one rotation direction ofthe rotor R, which is embodied as a sleeve-shaped external rotor.

With this motor design, the axes A1 to A4 form four 90° segments each ofwhich is to accommodate two respective permanent magnet poles M1 and M2,M3 and M4, M5 and M6, and M7 and M8 of the rotor R and two respectivemagnet poles P1 and P2, P3 and P4, P5 and P6, and P7 and P8, as shown inFIGS. 3 and 4. Since the formation of pole pairs should extend over polepairs of the stator St which are respectively offset by two polespacings, according to the invention, the magnet poles P1 and P3, P2 andP4, P5 and P7, and P6 and P8 must be provided with teeth which arerespectively offset to one another in order to achieve a compensation ofthe torque.

FIGS. 1 to 4 show an exemplary embodiment in which the fine gearingteeth always extend over the entire air gap surface of the magnet polesP1 to P8 and are embodied with identical and uniform tooth spacing. Thismeans that the width of the teeth Stand the tooth spaces of the statorare the same size.

In order to achieve the design of the motor outlined in FIG. 4, forexample the 90° segment, which is oriented toward the permanent magnetpoles M7 and M8, is provided with a fine gearing Vz1, as shown in FIG.1, wherein the leading edge of a tooth is aligned with the axis A1. Thefine gearing Vz3 which is associated with the permanent magnet poles M3and M4, is correspondingly designed, as shown by the leading edge of atooth that is aligned with the axis A3.

The 90° segments that are associated with the permanent magnet poles M1and M2 as well as M5 and M6 have fine gearings Vz2 and Vz4, which areoffset by half a tooth spacing in relation to the axes A2 and A4. If theteeth Z and the tooth spaces ZL have a uniform width a, then the offsetis equal to a, i.e. the fine gearings Vz2 and Vz4 are disposed so that aleading edge is aligned with the axes A2 and A4, as can be seen in FIG.2. The offset a therefore occurs in the pole pairs P1 and P3, P2 and P4,P5 and P7, and P6 and P8. The pole formation therefore is achieved viamagnet poles which are offset by two pole spacings of the stator St.This produces alternating wide teeth and wide tooth spaces at theadjoining points between the 90° segments.

If the solid stator according to FIG. 3 is punched out, then the magnetpoles P1 to P8 according to FIG. 4 are produced, wherein the finegearings Vz1, Vz2, Vz3, and Vz4 are divided into two identical (partial)fine gearings Vz11 and Vz12, Vz21 and Vz22, Vz31 and Vz32, and Vz41 andVz42, wherein the offset a between the fine gearings Vz11 and Vz21, Vz12and Vz22, Vz31 and Vz41, and Vz32 and Vz42 is retained and contributesto the compensation of the detent moment over the entire circumference.

In the exemplary embodiment, the permanent magnet poles M1 to M8 areconstituted by two-pole annular segment permanent magnets which arealigned with their neutral center axes on the axis A1 to A4 and arealigned with their poles in the same direction toward the circumferenceso that different poles of the annular segment permanent magnetsrespectively adjoin one another in the pole spaces of the rotor R. Therotor can also be constructed with multi-pole (>2) annular segmentpermanent magnets.

In the exemplary embodiment, the stator St and rotor R have the samenumber of ç=8 poles. The number of poles can also be less or more, itmerely has to be an even number. The number of poles of the stator Stcan also differ from the number of poles of the rotor R. The permanentmagnet poles M1 to M8 of the rotor R can also be constituted byindividual permanent magnets that are magnetized in single-pole fashion.

For the motor embodied according to FIG. 4, FIG. 5 once again shows theoffset a between the fine gearings Vz21 and Vz31 of the magnet poles P1and P3, which are shown in a view with reference to the permanent magnetpoles M1 and M3. If the permanent magnet poles M1 and M3 are embodied asindividual permanent magnets, then a leading edge of a tooth Z of thefine gearing Vz31 is aligned with the trailing edge of the permanentmagnet pole M3 and a leading edge of a tooth space ZL of the gearingVz21 is aligned with the trailing edge of the permanent magnet pole M1and the fine gearings Vz21 and Vz31 coincide with one another via thepole widths of the magnet poles P1 and P3 and of the permanent magnetpoles M1 and M3.

The magnet poles P1 and P3 are disposed at a distance (n+2) T, where n=1 or 2 and T is the pole spacing.

The fine gearing teeth, however, can also extend over only a partialcircumference region of the magnet poles P1 to P8. In this connection,the partial circumference regions of the pole pairs are as a rulematched to one another, i.e. they are selected so as to be equivalent tothe magnet poles of the pole pairs.

The tooth spacing with uniformly embodied teeth Z and tooth spaces isalso not absolutely necessary. In order to increase the compensationpossibilities, it is possible to offset only a part of the teeth andtooth spaces from one another. Furthermore, the width of the teeth andthe tooth spaces in the fine gearings can vary, at least in part. Inthis connection, it can be advantageous if the teeth Z of the finegearing of the one magnet pole are supplementary to the tooth spaces ZLof the fine gearing of the other magnet pole of the pole pairs. It isclear from this that there are numerous possibilities for influencingthe torque, which can be carried out solely by means of the stampingprocess of the stator St indicated in FIG. 3. In this connection, thesymmetrical basic design of the stator St is essentially retained. Theonly thing that changes is the fine gearing on the air gap surfaces ofthe magnet poles P1 to P8.

As shown by FIG. 6, the pole pair formation on the stator St can also becarried out by means of diametrically opposed pole pairs, as representedby the magnet poles P1 and P5. The fine gearings Vz21 and Vz41 in thisconnection are offset from each other by half a tooth spacing, as can beseen from their leading edges in relation to the trailing edges of thepermanent magnet poles M1 and M5.

The pole pair formation can also be carried out by means of adjacentmagnet poles, i.e. magnet poles that are offset by one pole spacing,e.g. P1 and P2 through P7 and P8. In addition, the pole pair formationcan be realized solely by means of the stamping process of the stator Stshown in FIG. 3. The number of the teeth of the fine gearings ispreferably greater than the number of the poles of the stator St and thedepths of the teeth Z and the tooth spaces ZL in the radial direction isgreater than or equal to the air gap width.

In any case, the design of the motor remains simple and can be easilyachieved. There are numerous possibilities of varying effectiveness forthe compensation of the detent moment. In each instance, a uniform,low-noise operation of the motor is achieved.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A motor with a stator (St) that has a number of magnetpoles (P1 to P8) and a rotor (R) with a corresponding number ofpermanent magnet poles (M1 to M8), in which an air gap is formed in theregion between the stator (St) and rotor (R), the stator is providedwith gearing teeth in order to reduce a torque between the stator androtor, wherein the pole structure of the stator (St) and rotor (R) isdesigned to be essentially symmetrical in a circumferential directionand the magnet poles (P1 to P8) of the stator (St) are provided at leastover a partial region of the air gap with the gearing teeth, and whereinthe magnet poles (P1 to P8) of the stator (St) constitute pole pairs inwhich the gearing teeth are disposed offset from one another at least inpartial circumferential regions.
 2. The motor according to claim 1wherein the number of the magnet poles (P1 to P8) of the stator (St) ismatched to the number of the permanent magnet poles (M1; M8) of therotor (R).
 3. The motor according to claim 2, wherein the offset of thegearing teeth of the pole pairs preferably correspond to half a spacingof the gearing teeth.
 4. The motor according to claim 2 wherein thepermanent magnet poles (M1 to M8) of the rotor (R) are constituted byindividual permanent magnets distributed uniformly over thecircumference of the rotor (R), which have an alternating polarity inthe circumferential direction.
 5. The motor according to claim 2,wherein the permanent magnet poles (M1 to M8) of the rotor (R) areconstituted by a number of two-pole annular segment permanent magnetsdistributed uniformly over a circumference of the rotor (R), which aredisposed with their poles in a same direction toward the circumference.6. The motor according to claim 1, wherein the offset of the gearingteeth of the pole pairs preferably correspond to half a spacing of thegearing teeth.
 7. The motor according to claim 1, wherein the stator(St) is embodied as an internal stator and the rotor (R) is embodied asan external rotor.
 8. The motor according to claim 1 wherein thepermanent magnet poles (M1 to M8) of the rotor (R) are constituted byindividual permanent magnets distributed uniformly over thecircumference of the rotor (R), which have an alternating polarity inthe circumferential direction.
 9. The motor according to claim 8,wherein the individual permanent magnets are magnetized in a single-polemanner.
 10. The motor according to claim 1, wherein the permanent magnetpoles (M1 to M8) of the rotor (R) are constituted by a number oftwo-pole annular segment permanent magnets distributed uniformly over acircumference of the rotor (R), which are disposed with their poles in asame direction toward the circumference.
 11. The motor according toclaim 10, wherein the permanent magnet poles (M1 to M8) of the rotor (R)are constituted by multi-pole annular segment permanent magnets.
 12. Themotor according to claim 1, wherein the gearing teeth are embodied asmeander-shaped.
 13. The motor according to claim 12, wherein the teeth(Z) and the spaces (ZL) of the gearing teeth have identical widths andidentical depths.
 14. The motor according to claim 12, wherein the teeth(Z) and spaces (ZL) of the one pole change in the same manner at leastin a partial circumference region.
 15. The motor according to claim 12,wherein the teeth (Z) and the spaces (ZL) of the gearing teeth havedifferent widths but have identical depths and are supplementary to eachother in the pole pairs.
 16. The motor according to claim 12, whereinthe teeth (Z) and spaces (ZL) of the one pole change in the same mannerat least in a partial circumference region.
 17. The motor according toclaim 1, wherein the number of the teeth (Z) and tooth spaces (ZL) ofthe gearing teeth is an integral multiple of the number of the polepairs formed.
 18. The motor according to claim 1, wherein the gearingteeth of said pole pairs of the stator (St), which are formed ofrespectively adjacent or diametrically opposed magnet poles, are offsetin relation to one another.
 19. The motor according to claim 1, whereinthe gearing teeth of said pole pairs of the stator (St), which areformed of magnet poles respectively offset by two pole spacings, areoffset in relation to one another.
 20. The motor according to claim 1,wherein the depths of the teeth (Z) and the tooth spaces (ZL) aregreater than or approximately equal to the air gap width between thestator (St) and the rotor (R).